Power over Wi-Fi: The end of IoT-sensor batteries?

Harnessing energy inherent in Wi-Fi or Bluetooth radio waves to power remote, wireless, Internet of Things (IoT) sensors — and also communicate with the devices at the same time — is a big-ticket item on IoT want-lists. Advantages include no batteries, thus reducing costs, size and weight.

The key to achieving it functionally, some scientists say, is in converting AC waveforms to DC voltage, combined with the use of new materials. Researchers at Massachusetts Institute of Technology, along with some collaborators, say they’ve made a breakthrough in this area. Interestingly, it also includes scaling potential.

“What if we could develop electronic systems that we wrap around a bridge or cover an entire highway, or the walls of our office and bring electronic intelligence to everything around us?” says Tomás Palacios, a professor in the Department of Electrical Engineering and Computer Science and director of the MIT/MTL Center for Graphene Devices and 2D Systems in the Microsystems Technology Laboratories, in an article in MIT News.

Palacios says “rectennas,” (as the AC-signal-to-DC-power devices are called), if they were made of a special, couple-atoms-thick 2-D material called molybdenum disulfide (MoS₂) would efficiently convert signals to DC from regular wireless, creating usable power, and they could do it large-scale if wanted.

The researchers believe that harvesting 150 microwatts of power (the power level of a typical Wi-Fi signal) with one of the rectennas could produce around 40 microwatts of electricity—enough to power a chip. Scaling the system to a vehicle, data center hall, or similar-sized setup, which they say is possible in part because their MoS₂ material is thin and flexible, would conceivably generate commensurate power.

The researchers also say the non-rigid, battery-free system is better than others’ attempts at rectennas because they capture “daily” signals such as “Wi-Fi, Bluetooth, cellular LTE, and many others,” says Xu Zhang, of collaborator Carnegie Mellon University, in the article. The other Radio Frequency-to-power converters, which are thick and non-flexible, aren’t wideband enough, the groups say.

Of course, radio waves already power some chips. RFID tags are an example. But those solutions are limited in their power and, therefore, range and bandwidth, which is why the search is on for something better.

Battery-free Bluetooth stickers on the way

A chip startup called Wiliot, claiming Amazon and Samsung funding among other benefactors, says it’s getting ready to launch battery-free Bluetooth stickers. The company’s postage-stamp-sized, tag-like device uses an ARM processor for “scavenging energy from ambient radio frequencies,” it said in a press release last month. The potentially disposable chip is aimed at connecting products to networks. An encrypted tag like that could also communicate sensor data with other IoT devices. The goal is to recycle the radiation around us, the company says.

Other, battery-free, IoT-sensor angles are being attempted, too. I wrote last year, about thermal resonating, another MIT project. It harvests untapped energy that’s created by ambient temperature fluctuations as night and day transitions. About 1.3 milliwatts of power was generated in experiments—enough to power a radio. Energy from vibration, or impact and shock is another angle being proposed by some.

Solar photovoltaic panels are, of course, the most commonly found ambient power collector, but those power sources won’t work in the dark, thus need a battery in IoT implementations, unlike the aforementioned no-battery solutions. Solar isn’t going to kill-off the battery anytime soon.

Adding to the mix, Wiliot also says IoT radio power-collectors should be disposable. “We believe that disposable electronics based on battery-free, low-cost systems are the foundation for future IoT systems,” Tal Tamir, of Wiliot, says in the release. “We are on the edge of dramatically changing the way products are made, and how they are used and recycled,” he says.